This invention relates to magnetic thin film heads, especially multi-track magnetic thin film heads having characteristics of less cross talk and less impedance noise on a reproducing mode, and a method of producing the same.
In the prior art, multi-track magnetic thin film heads have been used especially for recording a digital signal on a recording medium, for example, a magnetic disc, a magnetic sheet, a magnetic tape, etc. However, in using them for recording/reproducing an analog signal, there are some problems, for example, the cross talk from adjacent magnetic tracks, and the impedance noise on the reproducing mode.
Japanese Laid-Open Application No. 58.212616, laid open on Dec. 10, 1983, discloses an example of the prior art. FIGS. 1A, 1B and 1C show a structure of the multi-track magnetic thin film heads disclosed in the application. FIG. 1A depicts a plane view of the multi-track magnetic thin film heads including two magnetic heads. FIG. 1B and 1C show a sectional figure of an A--A' section in FIG. 1A and a front view from the B direction in FIG. 1A, respectively. Referring to FIGS. 1A, 1B and 1C, the numerals 1 and 2 denote a non-magnetic substrate and a lower magnetic core formed on the non-magnetic substrate 1, respectively. On the lower magnetic core, a first insulator 3a is deposited. Next, first layer coils 7a and 7b having a plane shape shown in FIG. 1A are formed on the first insulator 3a. Then, a second insulator 3b is superimposed on them without covering contact parts 10a and 10b. After that, second layer coils 8a and 8b, which are connected to the first layer coils 7a and 7b at the contact parts 10a and 10b, respectively, are formed on the second insulator 3b. Further, a third insulator 3c is superimposed on them, and upper magnetic cores 4a and 4b are deposited on the third insulator 3c. The numeral 5 designates a protective layer. In this configuration magnetic gaps of the heads are constructed by the first, second and third insulators 3a, 3b and 3c, and a track width and a gap length of each head are determined by a width T of the upper magnetic core 4a (4b) and a length Q, which is equal to a total thickness of the first, second and third insulators 3a, 3b and 3c, respectively. A track pitch of adjacent tracks is determined by a length P. As usual, the magnetic gap at a front part of the head is called a front gap, and the magnetic gap indicated by the numeral 9a (9b) is called a back gap. It is well known that there is another type of head, in which the upper magnetic core is connected to the lower magnetic core by a through-hole at a back gap part as shown by the broken line in FIG. 1B.
As briefly mentioned above, in this prior art, there is the cross talk from the adjacent tracks because of a continuity of the lower magnetic core 2 of the heads, and there is the impedance noise on the reproducing mode because it is impossible to use a large space for the coil and the resistance of the coil becomes higher. Further, there is a phase interference in a reproduced signal from the heads, caused by a contour effect of pseudo magnetic gaps, which are mainly formed by the lower edge of the lower magnetic core 2.